 
 
 
9.1.12  Substituting a variable by a value
The | operator is an infixed operator
that evaluates an expression after giving values to some variables.
It does not evaluate the expression before the variables are replaced by the
requested values.
- 
| is an infixed operator, hence it takes two arguments:
- 
expr, an expression depending on one or more
variables on the left hand side.
- x1=a1, ldots; an equality or
sequence of several equalities.
 
- expr|x1=a1,… returns the expression
expr with x1 replaced by a1, etc.
Examples
The command lines below work even if a and/or b
have been assigned.
 
 
